`@safe` by default. What about `@pure` and `immutable` by default?

[Atila Neves]

On Tuesday, 16 April 2019 at 03:59:38 UTC, Mike Franklin wrote:
> I think I may have found a simple migration path to @safe by 
> default.  I'm still thinking it through, but if I can justify 
> it, I will write a DIP.
>
> `@safe` by default is a no-brainer in my opinion, but `pure` 
> and `immutable` by default are less obvious.  With the 
> aforementioned potential DIP, I have an opportunity to correct 
> purity and mutability defaults as well...but is that something 
> we want to do?
>
> Can anyone save me some trouble and articulate why it would be 
> bad to have `pure` and/or `immutable` by default?
>
> Thanks,
> Mike

I think that `@safe` and `pure` should be the default, but not 
`immutable`. It's too restrictive. I'd make it `const` by 
default. I'm not *too* bothere about it though, because I have to 
write something before the variable's name to declare it anyway, 
so I myself just default to writing `const` instead of `auto`. 
The exception in nearly every case that isn't dealing with a 
dependency that isn't const-correct is ranges.

As mentioned elsewhere on this thread, for `pure` to be the 
default we need to be able to negate it.